PERSEUS is an open source technology whose aim is to secure any kind of communication streams against illegitimate or abusive eavesdropping except for Nation State Security offices, provided that a suitable, huge computing power is used (from tens of hours with a supercomputer). PERSEUS enables to provide at the same time users' needs for privacy and confidentiality while preserving the ability of security agencies (police, defense, national security...) to eavesdrop communications of really bad actors (terrorists, child pornographs...).